Sometimes, on a rather boring and run-of-the-mill Monday, I get news in the submission queue which just puts a gigantic smile on my face. We've talkedabout the Raspberry Pi before on OSNews, and other than reporting that everything's on track for a Christmas launch, it has also been announced that the Raspberry Pi will be able to run... RISC OS. A British educational ARM board running RISC OS? We have come full circle. And I couldn't be happier. Update: Theo Markettos emailed me with two corrections - Markettos isn't actually a representative of the Raspberry Pi Foundation, and the quoted bits are transcribed, they're not Markettos' literal words. Thanks for clearing that up!

Arguably, the RISC OS camp didn't realize it, they just got lucky by relatively cheap and generic ARM hardware becoming popular for some things.

The Amiga camp moved to PPC back when PPC was viable, and there were, IIRC, a couple attempts to move to Macs just as the PPC Mac was dying. Now, it's not a popular platform for this sort of thing, so they have to make their own hardware - just as the Acorn community did 5-10 years ago.

Perhaps, though RISC OS camp does seem to jump relatively quickly on inexpensive almost-retail hardware; they saw their chance in targeting such machine.

The Amiga camp did it way late (excluding AROS, but it needs its time). Only recently MorphOS runs on some old, "surplus" Macs, while Powermacs were available for quite some time. And I think it's more appropriate to discuss those, whole machines, when it comes to past viability; not simply the PPC CPU - which anyway was, for many years, essentially just a coprocessor.
(the whole movement seemed more about few small manufacturers feeding on the leftovers of Amiga following, to keep them alive a bit longer; while perhaps there were more optimal routes - consider how Amithlon, in its days, smoked pretty much every "true Amiga" hardware, for much lesser price, and IIRC it could provide a gradual & transparent to the OS shift towards x86-compiled code; but, the community had strong ideological issues with x86... ~"well, Apple doesn't use them, they use what's best" turned out funny)

Of course, for a long time, there were three kinds of RISC OS machine:

Old RiscPCs with somewhat faster CPU cards (or just the original CPU cards - those are the elderly that keep the commercial RISC OS world afloat)
Newer custom-designed machines, sometimes with their development partially subsidized by part of it being part of an "ARM Linux devkit" that's low-volume, expensive hardware (one of those, with a far slower CPU than the Raspberry Pi, is still available - the better Iyonix was killed off due to RoHS issues)
Windows machines running Virtual RiscPC (and one company is still selling those) - and these get the "but it's not ARM" treatment

They were pretty quick about jumping on the Beagleboard, though, when it became available. Actually, it was the "ZOMG WE NEED A RISC OS LAPTOP" mentality (the only production RISC OS laptop had an ARM3, so it was woefully out of date) that led them to a port to the Pandora, which led them to the Beagleboard as their dev platform.